﻿using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Linq.Expressions;
using System.Collections.ObjectModel;

namespace EasyDev.Expressions
{
        public abstract class ExpressionVisitor
        {
                protected ExpressionVisitor()
                {
                }

                protected virtual Expression Visit(Expression exp)
                {
                        if (exp == null)
                                return exp;
                        switch (exp.NodeType)
                        {
                                case ExpressionType.Negate:
                                case ExpressionType.NegateChecked:
                                case ExpressionType.Not:
                                case ExpressionType.Convert:
                                case ExpressionType.ConvertChecked:
                                case ExpressionType.ArrayLength:
                                case ExpressionType.Quote:
                                case ExpressionType.TypeAs: return this.VisitUnary((UnaryExpression)exp);
                                case ExpressionType.Add:
                                case ExpressionType.AddChecked:
                                case ExpressionType.Subtract:
                                case ExpressionType.SubtractChecked:
                                case ExpressionType.Multiply:
                                case ExpressionType.MultiplyChecked:
                                case ExpressionType.Divide:
                                case ExpressionType.Modulo:
                                case ExpressionType.And:
                                case ExpressionType.AndAlso:
                                case ExpressionType.Or:
                                case ExpressionType.OrElse:
                                case ExpressionType.LessThan:
                                case ExpressionType.LessThanOrEqual:
                                case ExpressionType.GreaterThan:
                                case ExpressionType.GreaterThanOrEqual:
                                case ExpressionType.Equal:
                                case ExpressionType.NotEqual:
                                case ExpressionType.Coalesce:
                                case ExpressionType.ArrayIndex:
                                case ExpressionType.RightShift:
                                case ExpressionType.LeftShift:
                                case ExpressionType.ExclusiveOr: return this.VisitBinary((BinaryExpression)exp);
                                case ExpressionType.TypeIs: return this.VisitTypeIs((TypeBinaryExpression)exp);
                                case ExpressionType.Conditional: return this.VisitConditional((ConditionalExpression)exp);
                                case ExpressionType.Constant: return this.VisitConstant((ConstantExpression)exp);
                                case ExpressionType.Parameter: return this.VisitParameter((ParameterExpression)exp);
                                case ExpressionType.MemberAccess: return this.VisitMemberAccess((MemberExpression)exp);
                                case ExpressionType.Call: return this.VisitMethodCall((MethodCallExpression)exp);
                                case ExpressionType.Lambda: return this.VisitLambda((LambdaExpression)exp);
                                case ExpressionType.New: return this.VisitNew((NewExpression)exp);
                                case ExpressionType.NewArrayInit:
                                case ExpressionType.NewArrayBounds: return this.VisitNewArray((NewArrayExpression)exp);
                                case ExpressionType.Invoke: return this.VisitInvocation((InvocationExpression)exp);
                                case ExpressionType.MemberInit: return this.VisitMemberInit((MemberInitExpression)exp);
                                case ExpressionType.ListInit: return this.VisitListInit((ListInitExpression)exp);
                                default: throw new Exception(string.Format("Unhandled expression type: '{0}'", exp.NodeType));
                        }
                }

                protected virtual MemberBinding VisitBinding(MemberBinding binding)
                {
                        switch (binding.BindingType)
                        {
                                case MemberBindingType.Assignment:
                                        return this.VisitMemberAssignment((MemberAssignment)binding);
                                case MemberBindingType.MemberBinding:
                                        return this.VisitMemberMemberBinding((MemberMemberBinding)binding);
                                case MemberBindingType.ListBinding:
                                        return this.VisitMemberListBinding((MemberListBinding)binding);
                                default:
                                        throw new Exception(string.Format("Unhandled binding type '{0}'", binding.BindingType));
                        }
                }

                protected virtual ElementInit VisitElementInitializer(ElementInit initializer)
                {
                        ReadOnlyCollection<Expression> arguments = this.VisitExpressionList(initializer.Arguments);
                        if (arguments != initializer.Arguments)
                        {
                                return Expression.ElementInit(initializer.AddMethod, arguments);
                        }
                        return initializer;
                }

                protected virtual Expression VisitUnary(UnaryExpression u)
                {
                        Expression operand = this.Visit(u.Operand);
                        if (operand != u.Operand)
                        {
                                return Expression.MakeUnary(u.NodeType, operand, u.Type, u.Method);
                        }
                        return u;
                }

                protected virtual Expression VisitBinary(BinaryExpression b)
                {
                        Expression left = this.Visit(b.Left);
                        Expression right = this.Visit(b.Right);
                        Expression conversion = this.Visit(b.Conversion);
                        if (left != b.Left || right != b.Right || conversion != b.Conversion)
                        {
                                if (b.NodeType == ExpressionType.Coalesce && b.Conversion != null)
                                        return Expression.Coalesce(left, right, conversion as LambdaExpression);
                                else
                                        return Expression.MakeBinary(b.NodeType, left, right, b.IsLiftedToNull, b.Method);
                        }
                        return b;
                }

                protected virtual Expression VisitTypeIs(TypeBinaryExpression b)
                {
                        Expression expr = this.Visit(b.Expression);
                        if (expr != b.Expression)
                        {
                                return Expression.TypeIs(expr, b.TypeOperand);
                        }
                        return b;
                }

                protected virtual Expression VisitConstant(ConstantExpression c)
                {
                        return c;
                }

                protected virtual Expression VisitConditional(ConditionalExpression c)
                {
                        Expression test = this.Visit(c.Test);
                        Expression ifTrue = this.Visit(c.IfTrue);
                        Expression ifFalse = this.Visit(c.IfFalse);
                        if (test != c.Test || ifTrue != c.IfTrue || ifFalse != c.IfFalse)
                        {
                                return Expression.Condition(test, ifTrue, ifFalse);
                        }
                        return c;
                }

                protected virtual Expression VisitParameter(ParameterExpression p)
                {
                        return p;
                }

                protected virtual Expression VisitMemberAccess(MemberExpression m)
                {
                        Expression exp = this.Visit(m.Expression);
                        if (exp != m.Expression)
                        {
                                return Expression.MakeMemberAccess(exp, m.Member);
                        }
                        return m;
                }

                protected virtual Expression VisitMethodCall(MethodCallExpression m)
                {
                        Expression obj = this.Visit(m.Object);
                        IEnumerable<Expression> args = this.VisitExpressionList(m.Arguments);
                        if (obj != m.Object || args != m.Arguments)
                        {
                                return Expression.Call(obj, m.Method, args);
                        }
                        return m;
                }

                protected virtual ReadOnlyCollection<Expression> VisitExpressionList(ReadOnlyCollection<Expression> original)
                {
                        List<Expression> list = null;
                        for (int i = 0, n = original.Count; i < n; i++)
                        {
                                Expression p = this.Visit(original[i]);
                                if (list != null)
                                {
                                        list.Add(p);
                                }
                                else if (p != original[i])
                                {
                                        list = new List<Expression>(n);
                                        for (int j = 0; j < i; j++)
                                        {
                                                list.Add(original[j]);
                                        }
                                        list.Add(p);
                                }
                        }
                        if (list != null)
                        {
                                return list.AsReadOnly();
                        }
                        return original;
                }

                protected virtual MemberAssignment VisitMemberAssignment(MemberAssignment assignment)
                {
                        Expression e = this.Visit(assignment.Expression);
                        if (e != assignment.Expression)
                        {
                                return Expression.Bind(assignment.Member, e);
                        }
                        return assignment;
                }

                protected virtual MemberMemberBinding VisitMemberMemberBinding(MemberMemberBinding binding)
                {
                        IEnumerable<MemberBinding> bindings = this.VisitBindingList(binding.Bindings);
                        if (bindings != binding.Bindings)
                        {
                                return Expression.MemberBind(binding.Member, bindings);
                        }
                        return binding;
                }

                protected virtual MemberListBinding VisitMemberListBinding(MemberListBinding binding)
                {
                        IEnumerable<ElementInit> initializers = this.VisitElementInitializerList(binding.Initializers);
                        if (initializers != binding.Initializers)
                        {
                                return Expression.ListBind(binding.Member, initializers);
                        }
                        return binding;
                }

                protected virtual IEnumerable<MemberBinding> VisitBindingList(ReadOnlyCollection<MemberBinding> original)
                {
                        List<MemberBinding> list = null;
                        for (int i = 0, n = original.Count; i < n; i++)
                        {
                                MemberBinding b = this.VisitBinding(original[i]);
                                if (list != null)
                                {
                                        list.Add(b);
                                }
                                else if (b != original[i])
                                {
                                        list = new List<MemberBinding>(n);
                                        for (int j = 0; j < i; j++)
                                        {
                                                list.Add(original[j]);
                                        }
                                        list.Add(b);
                                }
                        }
                        if (list != null)
                                return list;
                        return original;
                }

                protected virtual IEnumerable<ElementInit> VisitElementInitializerList(ReadOnlyCollection<ElementInit> original)
                {
                        List<ElementInit> list = null;
                        for (int i = 0, n = original.Count; i < n; i++)
                        {
                                ElementInit init = this.VisitElementInitializer(original[i]);
                                if (list != null)
                                {
                                        list.Add(init);
                                }
                                else if (init != original[i])
                                {
                                        list = new List<ElementInit>(n);
                                        for (int j = 0; j < i; j++)
                                        {
                                                list.Add(original[j]);
                                        }
                                        list.Add(init);
                                }
                        }
                        if (list != null)
                                return list;
                        return original;
                }

                protected virtual Expression VisitLambda(LambdaExpression lambda)
                {
                        Expression body = this.Visit(lambda.Body);
                        if (body != lambda.Body)
                        {
                                return Expression.Lambda(lambda.Type, body, lambda.Parameters);
                        }
                        return lambda;
                }

                protected virtual NewExpression VisitNew(NewExpression nex)
                {
                        IEnumerable<Expression> args = this.VisitExpressionList(nex.Arguments);
                        if (args != nex.Arguments)
                        {
                                if (nex.Members != null)
                                        return Expression.New(nex.Constructor, args, nex.Members);
                                else
                                        return Expression.New(nex.Constructor, args);
                        }
                        return nex;
                }

                protected virtual Expression VisitMemberInit(MemberInitExpression init)
                {
                        NewExpression n = this.VisitNew(init.NewExpression);
                        IEnumerable<MemberBinding> bindings = this.VisitBindingList(init.Bindings);
                        if (n != init.NewExpression || bindings != init.Bindings)
                        {
                                return Expression.MemberInit(n, bindings);
                        }
                        return init;
                }

                protected virtual Expression VisitListInit(ListInitExpression init)
                {
                        NewExpression n = this.VisitNew(init.NewExpression);
                        IEnumerable<ElementInit> initializers = this.VisitElementInitializerList(init.Initializers);
                        if (n != init.NewExpression || initializers != init.Initializers)
                        {
                                return Expression.ListInit(n, initializers);
                        }
                        return init;
                }

                protected virtual Expression VisitNewArray(NewArrayExpression na)
                {
                        IEnumerable<Expression> exprs = this.VisitExpressionList(na.Expressions);
                        if (exprs != na.Expressions)
                        {
                                if (na.NodeType == ExpressionType.NewArrayInit)
                                {
                                        return Expression.NewArrayInit(na.Type.GetElementType(), exprs);
                                }
                                else
                                {
                                        return Expression.NewArrayBounds(na.Type.GetElementType(), exprs);
                                }
                        }
                        return na;
                }

                protected virtual Expression VisitInvocation(InvocationExpression iv)
                {
                        IEnumerable<Expression> args = this.VisitExpressionList(iv.Arguments);
                        Expression expr = this.Visit(iv.Expression);
                        if (args != iv.Arguments || expr != iv.Expression)
                        {
                                return Expression.Invoke(expr, args);
                        }
                        return iv;
                }
        }
}
